Large optical cross-connect systems are used to switch optical signals between fiber links without conversion into the electrical domain. These systems are useful for dynamic capacity allocation and network recovery, for example.
The optical cross-connect switch systems are implemented on a variety of platforms. Presently, microelectromechanical systems (MEMS)-based switches using tilt mirror arrays are being pursued by a number of entities. The individual mirrors are used to couple light exiting from one user fiber link into another user fiber link.
One issue surrounding the deployment of these optical cross-connect switch systems concerns robustness. The switch fabrics are large. This makes it difficult to maintain the requirement that every path or connection through the fabric be operational at all times. For example, it is not uncommon for a few of the individual tilt mirrors in an array to become non-operational. This will have the effect of removing potential connections.
One solution to this problem relies on the use of redundant switch fabrics. If the connection is not possible between two user fibers with the primary switch fabric, the connection is made with the redundant switch fabric.
In order to switch between the primary and redundant systems, line card modules are used in conjunction with these switching systems. They have the capability of directing the optical signal from a user fiber either to the primary or redundant system. More generally, such line card protection modules are used in other applications where the ability to switch an optical signal between two systems is required, such as between primary and redundant rings in a SONET system.
In a common line card implementation, an optical signal from a user fiber is received at an input port of the protector module and switched between two output fiber links. Typically, a tap is provided to monitor the input signal. A two-by-two (2xc3x972) switch is provided to route the input signal in addition to a monitoring signal from one of the switching systems to a monitoring diode.
Signals from the primary and redundant systems are handled by a second 2xc3x972 switch. Specifically, the signal from either the primary or the redundant system is connected to another user fiber at an output port of the module. The other system is connected to a laser diode to thereby probe the operation of the primary or redundant system that is not currently in use with the monitoring signal. Typically, a monitoring port is used to detect the output from this laser. Similarly, another tap is provided to detect the signal that is transmitted to the output port.
In the past, line card protection modules have been offered with only relatively low levels of integration. Moreover, the interconnections, such as signal taps, were provided through fiber couplers. These factors made the modules large and expense to manufacture.
The present invention is directed to an integrated optical line card protection module. It is notable in that it uses free-space optical links to thereby increase the level of integration while decreasing footprint.
In general, according to one aspect, the invention features an optical line card protection module. The module comprises a bench, a user-side interface to an array of user fibers, i.e., the fibers that carry optical signals to and from another system, and a device-side interface to an array of device fibers, i.e., the fibers that carry optical signals to and from the primary and redundant devices, for example. A monitoring signal generator is provided on the bench that provides monitoring signals. A monitoring signal detector is also on the bench that detects the monitoring signals. Finally, a beam switching system is provided that selectively connects the user fibers to the device fibers of the primary device or the device fibers of the redundant device.
In one embodiment, the user-side interface and the device-side interface comprise separate fiber mounting blocks for respectively mounting the endfaces of the user fibers and the endfaces of the device fibers to the bench. Further, a user-side lens array is preferably secured to the bench between the fiber endfaces of the user fibers and the beam switching system. This facilitates coupling of the optical signals between the beam switching system and the user fibers. Device-side lens array is also preferably secured to the bench between the fiber endfaces of the device fibers and the beam switching system.
In the current embodiment, the monitoring signal generator comprises at least one semiconductor device that is mounted on the bench. It can be a semiconductor laser or a light emitting diode. A generator lens array directs the monitoring signals from the semiconductor device to the beam switching system. In the present implementation, the beam switching system enables output beams to the user-side interface to be transmitted past the beam switching system in a first state and translates the beam in a second state. This allows the user fibers for the primary and redundant device to be arranged parallel to each other, providing an in-line system. In one implementation, the beam switching system comprises opposed tilt mirror arrays.
In general, according to another aspect, the line card protection module comprises user input signal tap detector arrays and/or user output signal tap detector arrays. These are located in the beam path between the user-side interface and the beam switching system to detect optical signals that are being transmitted between the user fibers and the beam switching system.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.